The region has been criticized for the length of time it allots for yellow-light intervals. Staff say their timing meets or exceeds provincial standards.

Warning light

By James Jackson, Chronicle staff

The Region of Waterloo says it times its yellow lights fairly and safely, taking into account all the variables that can influence safe stopping times.

“We are setting yellow appropriately, it’s accounting for the speed (and) it’s accounting for the length of time it takes for someone to perceive and react to a yellow,” said Thomas Schmidt, regional transportation commissioner.

“There isn’t a safety concern related to the length of yellow lights here in the Region of Waterloo.”

Currently, the region sets the length of yellow lights — referred to as a yellow light interval — at four seconds in areas with speed limits between 40 and 60 kilometres per hour. The interval increases to 4.2 seconds in a 70-km/h zone, and 5.4 seconds in an 80-km/h zone.

The region has been criticized for not taking real-world driving conditions into account, such as the fact most drivers drive above the posted speed limit.

Yet Schmidt said Waterloo meets or exceeds provincial guideline recommendations for the timing of yellow lights. The provincial minimum is based on a perception time of one second and assumes the driver is travelling the posted speed limit.

The region’s timing is also in line with what the National Cooperative Highway Research Program in the United States also suggested in a recent report.

The NCHRP recommends an approximately five-second increase in yellow times for every 10-km/h increase, starting at 3.3 seconds in a 40-km/h zone and ending at 5.2 seconds in an 80-km/h zone. The organization assumed drivers are travelling about 10 km/h over the posted limit.

An increase in yellow times would not necessarily lead to fewer crashes or injuries, Schmidt said, and the region already accounts for some real-world conditions by surpassing the provincial minimum.

Schmidt said it would be difficult and expensive to get real-time data of vehicle speeds for every intersection, and he said evidence suggests drivers on city routes are going approximately the posted limit, while others (such as those preparing to turn) are actually going much slower.

The design of streets influences the speed of traffic more than light intervals, said Schmidt.

He said wide-open roads tend to have higher traffic speeds than in-town routes.

When a light turns yellow, drivers approaching the intersection are sometimes caught in what traffic experts call the “dilemma zone.” There might not be enough time to make it through the intersection before the light turns red, but not enough space to safely stop, either.

Schmidt said lengthening the yellow would not solve the problem because some drivers would perceive the change in time and adjust their driving accordingly. It would also not solve the problem of drivers slamming on their brakes for a yellow and surprising a driver behind them, who thought there was enough time to drive through.

Lengthening the yellow interval would impact the carrying capacity of the intersection, potentially leading to backups in other directions, he said.

“Extending it would not make things safer and would not necessarily reduce red light running,” Schmidt said.

On top of the four-plus seconds for yellow lights, the region also employs a two-second all-red signal to give vehicles already in the intersection enough time to exit, meaning there is actually a gap of at least six seconds between when the light first turns yellow to when traffic in the other lanes get a green.

Drivers that enter an intersection while the light is still yellow but exit after it turns red will not be ticketed. Only drivers who enter the intersection after the light turns red are ticketed.

Schmidt said the times are constant throughout the region, whether there is a red light camera at the intersection or not.

Yellow light interval

Posted speed (km/h)

40

50

60

70

80

Provincial guidelines (seconds)

3

3.3

3.7

4.2

4.6

Region of Waterloo (seconds)

4

4

4

4.2

5.4

NCHRP report (seconds)

3.3

3.8

4.3

4.7

5.2

*The province and the region assume drivers are travelling the speed limit, while the NCHRP assumes drivers are travelling 10 km/h above the posted limit. All three assume a perception time of one second.